KVM: x86/xen: fix recursive deadlock in timer injection

The fast-path timer delivery introduced a recursive locking deadlock
when userspace configures a timer which has already expired and is
delivered immediately. The call to kvm_xen_inject_timer_irqs() can
call to kvm_xen_set_evtchn() which may take kvm->arch.xen.xen_lock,
which is already held in kvm_xen_vcpu_get_attr().

============================================
WARNING: possible recursive locking detected
6.8.0-smp--5e10b4d51d77-drs #232 Tainted: G O
--------------------------------------------
xen_shinfo_test/250013 is trying to acquire lock:
ffff938c9930cc30 (&kvm->arch.xen.xen_lock){+.+.}-{3:3}, at: kvm_xen_set_evtchn+0x74/0x170 [kvm]

but task is already holding lock:
ffff938c9930cc30 (&kvm->arch.xen.xen_lock){+.+.}-{3:3}, at: kvm_xen_vcpu_get_attr+0x38/0x250 [kvm]

Now that the gfn_to_pfn_cache has its own self-sufficient locking, its
callers no longer need to ensure serialization, so just stop taking
kvm->arch.xen.xen_lock from kvm_xen_set_evtchn().

Fixes: 77c9b9dea4fb ("KVM: x86/xen: Use fast path for Xen timer delivery")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240227115648.3104-6-dwmw2@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: remove WARN_ON_ONCE() with false positives in evtchn delivery

The kvm_xen_inject_vcpu_vector() function has a comment saying "the fast
version will always work for physical unicast", justifying its use of
kvm_irq_delivery_to_apic_fast() and the WARN_ON_ONCE() when that fails.

In fact that assumption isn't true if X2APIC isn't in use by the guest
and there is (8-bit x)APIC ID aliasing. A single "unicast" destination
APIC ID *may* then be delivered to multiple vCPUs. Remove the warning,
and in fact it might as well just call kvm_irq_delivery_to_apic().

Reported-by: Michal Luczaj <mhal@rbox.co>
Fixes: fde0451be8fb3 ("KVM: x86/xen: Support per-vCPU event channel upcall via local APIC")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240227115648.3104-4-dwmw2@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: inject vCPU upcall vector when local APIC is enabled

Linux guests since commit b1c3497e604d ("x86/xen: Add support for
HVMOP_set_evtchn_upcall_vector") in v6.0 onwards will use the per-vCPU
upcall vector when it's advertised in the Xen CPUID leaves.

This upcall is injected through the guest's local APIC as an MSI, unlike
the older system vector which was merely injected by the hypervisor any
time the CPU was able to receive an interrupt and the upcall_pending
flags is set in its vcpu_info.

Effectively, that makes the per-CPU upcall edge triggered instead of
level triggered, which results in the upcall being lost if the MSI is
delivered when the local APIC is *disabled*.

Xen checks the vcpu_info->evtchn_upcall_pending flag when the local APIC
for a vCPU is software enabled (in fact, on any write to the SPIV
register which doesn't disable the APIC). Do the same in KVM since KVM
doesn't provide a way for userspace to intervene and trap accesses to
the SPIV register of a local APIC emulated by KVM.

Fixes: fde0451be8fb3 ("KVM: x86/xen: Support per-vCPU event channel upcall via local APIC")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240227115648.3104-3-dwmw2@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: improve accuracy of Xen timers

A test program such as http://david.woodhou.se/timerlat.c confirms user
reports that timers are increasingly inaccurate as the lifetime of a
guest increases. Reporting the actual delay observed when asking for
100µs of sleep, it starts off OK on a newly-launched guest but gets
worse over time, giving incorrect sleep times:

root@ip-10-0-193-21:~# ./timerlat -c -n 5
00000000 latency 103243/100000 (3.2430%)
00000001 latency 103243/100000 (3.2430%)
00000002 latency 103242/100000 (3.2420%)
00000003 latency 103245/100000 (3.2450%)
00000004 latency 103245/100000 (3.2450%)

The biggest problem is that get_kvmclock_ns() returns inaccurate values
when the guest TSC is scaled. The guest sees a TSC value scaled from the
host TSC by a mul/shift conversion (hopefully done in hardware). The
guest then converts that guest TSC value into nanoseconds using the
mul/shift conversion given to it by the KVM pvclock information.

But get_kvmclock_ns() performs only a single conversion directly from
host TSC to nanoseconds, giving a different result. A test program at
http://david.woodhou.se/tsdrift.c demonstrates the cumulative error
over a day.

It's non-trivial to fix get_kvmclock_ns(), although I'll come back to
that. The actual guest hv_clock is per-CPU, and *theoretically* each
vCPU could be running at a *different* frequency. But this patch is
needed anyway because...

The other issue with Xen timers was that the code would snapshot the
host CLOCK_MONOTONIC at some point in time, and then... after a few
interrupts may have occurred, some preemption perhaps... would also read
the guest's kvmclock. Then it would proceed under the false assumption
that those two happened at the *same* time. Any time which *actually*
elapsed between reading the two clocks was introduced as inaccuracies
in the time at which the timer fired.

Fix it to use a variant of kvm_get_time_and_clockread(), which reads the
host TSC just *once*, then use the returned TSC value to calculate the
kvmclock (making sure to do that the way the guest would instead of
making the same mistake get_kvmclock_ns() does).

Sadly, hrtimers based on CLOCK_MONOTONIC_RAW are not supported, so Xen
timers still have to use CLOCK_MONOTONIC. In practice the difference
between the two won't matter over the timescales involved, as the
*absolute* values don't matter; just the delta.

This does mean a new variant of kvm_get_time_and_clockread() is needed;
called kvm_get_monotonic_and_clockread() because that's what it does.

Fixes: 536395260582 ("KVM: x86/xen: handle PV timers oneshot mode")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240227115648.3104-2-dwmw2@infradead.org
[sean: massage moved comment, tweak if statement formatting]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: allow vcpu_info content to be 'safely' copied

If the guest sets an explicit vcpu_info GPA then, for any of the first 32
vCPUs, the content of the default vcpu_info in the shared_info page must be
copied into the new location. Because this copy may race with event
delivery (which updates the 'evtchn_pending_sel' field in vcpu_info),
event delivery needs to be deferred until the copy is complete.

Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_xen
that is used in atomic context if the vcpu_info PFN cache has been
invalidated so that the update of vcpu_info can be deferred until the
cache can be refreshed (on vCPU thread's the way back into guest context).

Use this shadow if the vcpu_info cache has been *deactivated*, so that
the VMM can safely copy the vcpu_info content and then re-activate the
cache with the new GPA. To do this, stop considering an inactive vcpu_info
cache as a hard error in kvm_xen_set_evtchn_fast(), and let the existing
kvm_gpc_check() fail and kick the vCPU (if necessary).

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-21-paul@xen.org
[sean: add a bit of verbosity to the changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA

If the guest does not explicitly set the GPA of vcpu_info structure in
memory then, for guests with 32 vCPUs or fewer, the vcpu_info embedded
in the shared_info page may be used. As described in a previous commit,
the shared_info page is an overlay at a fixed HVA within the VMM, so in
this case it also more optimal to activate the vcpu_info cache with a
fixed HVA to avoid unnecessary invalidation if the guest memory layout
is modified.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-14-paul@xen.org
[sean: use kvm_gpc_is_{gpa,hva}_active()]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: allow shared_info to be mapped by fixed HVA

The shared_info page is not guest memory as such. It is a dedicated page
allocated by the VMM and overlaid onto guest memory in a GFN chosen by the
guest and specified in the XENMEM_add_to_physmap hypercall. The guest may
even request that shared_info be moved from one GFN to another by
re-issuing that hypercall, but the HVA is never going to change.

Because the shared_info page is an overlay the memory slots need to be
updated in response to the hypercall. However, memory slot adjustment is
not atomic and, whilst all vCPUs are paused, there is still the possibility
that events may be delivered (which requires the shared_info page to be
updated) whilst the shared_info GPA is absent. The HVA is never absent
though, so it makes much more sense to use that as the basis for the
kernel's mapping.

Hence add a new KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA attribute type for this
purpose and a KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA flag to advertize its
availability. Don't actually advertize it yet though. That will be done in
a subsequent patch, which will also add tests for the new attribute type.

Also update the KVM API documentation with the new attribute and also fix
it up to consistently refer to 'shared_info' (with the underscore).

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-13-paul@xen.org
[sean: store "hva" as a user pointer, use kvm_gpc_is_{gpa,hva}_active()]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is set

If the shared_info PFN cache has already been initialized then the content
of the shared_info page needs to be re-initialized whenever the guest
mode is (re)set.
Setting the guest mode is either done explicitly by the VMM via the
KVM_XEN_ATTR_TYPE_LONG_MODE attribute, or implicitly when the guest writes
the MSR to set up the hypercall page.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-12-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: separate initialization of shared_info cache and content

A subsequent patch will allow shared_info to be initialized using either a
GPA or a user-space (i.e. VMM) HVA. To make that patch cleaner, separate
the initialization of the shared_info content from the activation of the
pfncache.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-11-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: pfncache: remove KVM_GUEST_USES_PFN usage

As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
callers of kvm_gpc_init(), and for good reason: the implementation is
incomplete/broken. And it's not clear that there will ever be a user of
KVM_GUEST_USES_PFN, as coordinating vCPUs with mmu_notifier events is
non-trivial.

Remove KVM_GUEST_USES_PFN and all related code, e.g. dropping
KVM_GUEST_USES_PFN also makes the 'vcpu' argument redundant, to avoid
having to reason about broken code as __kvm_gpc_refresh() evolves.

Moreover, all existing callers specify KVM_HOST_USES_PFN so the usage
check in hva_to_pfn_retry() and hence the 'usage' argument to
kvm_gpc_init() are also redundant.

[1] https://lore.kernel.org/all/ZQiR8IpqOZrOpzHC@google.com

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-6-paul@xen.org
[sean: explicitly call out that guest usage is incomplete]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: pfncache: add a mark-dirty helper

At the moment pages are marked dirty by open-coded calls to
mark_page_dirty_in_slot(), directly deferefencing the gpa and memslot
from the cache. After a subsequent patch these may not always be set
so add a helper now so that caller will protected from the need to know
about this detail.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-5-paul@xen.org
[sean: decrease indentation, use gpa_to_gfn()]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: mark guest pages dirty with the pfncache lock held

Sampling gpa and memslot from an unlocked pfncache may yield inconsistent
values so, since there is no problem with calling mark_page_dirty_in_slot()
with the pfncache lock held, relocate the calls in
kvm_xen_update_runstate_guest() and kvm_xen_inject_pending_events()
accordingly.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-4-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT

Unless explicitly told to do so (by passing 'clocksource=tsc' and
'tsc=stable:socket', and then jumping through some hoops concerning
potential CPU hotplug) Xen will never use TSC as its clocksource.
Hence, by default, a Xen guest will not see PVCLOCK_TSC_STABLE_BIT set
in either the primary or secondary pvclock memory areas. This has
led to bugs in some guest kernels which only become evident if
PVCLOCK_TSC_STABLE_BIT *is* set in the pvclocks. Hence, to support
such guests, give the VMM a new Xen HVM config flag to tell KVM to
forcibly clear the bit in the Xen pvclocks.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20231102162128.2353459-1-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

eventfd: simplify eventfd_signal()

Ever since the eventfd type was introduced back in 2007 in commit
e1ad7468c77d ("signal/timer/event: eventfd core") the eventfd_signal()
function only ever passed 1 as a value for @n. There's no point in
keeping that additional argument.

Link: https://lore.kernel.org/r/20231122-vfs-eventfd-signal-v2-2-bd549b14ce0c@kernel.org
Acked-by: Xu Yilun <yilun.xu@intel.com>
Acked-by: Andrew Donnellan <ajd@linux.ibm.com> # ocxl
Acked-by: Eric Farman <farman@linux.ibm.com> # s390
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

KVM: x86: Refine calculation of guest wall clock to use a single TSC read

When populating the guest's PV wall clock information, KVM currently does
a simple 'kvm_get_real_ns() - get_kvmclock_ns(kvm)'. This is an antipattern
which should be avoided; when working with the relationship between two
clocks, it's never correct to obtain one of them "now" and then the other
at a slightly different "now" after an unspecified period of preemption
(which might not even be under the control of the kernel, if this is an
L1 hosting an L2 guest under nested virtualization).

Add a kvm_get_wall_clock_epoch() function to return the guest wall clock
epoch in nanoseconds using the same method as __get_kvmclock() — by using
kvm_get_walltime_and_clockread() to calculate both the wall clock and KVM
clock time from a *single* TSC reading.

The condition using get_cpu_tsc_khz() is equivalent to the version in
__get_kvmclock() which separately checks for the CONSTANT_TSC feature or
the per-CPU cpu_tsc_khz. Which is what get_cpu_tsc_khz() does anyway.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/bfc6d3d7cfb88c47481eabbf5a30a264c58c7789.camel@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: ignore the VCPU_SSHOTTMR_future flag

Upstream Xen now ignores _VCPU_SSHOTTMR_future[1], since the only guest
kernel ever to use it was buggy. By ignoring the flag the guest will
always get a callback if it sets a negative timeout which upstream Xen
has determined not to cause problems for any guest setting the flag.

[1] https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=19c6cbd909

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20231004174628.2073263-1-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: Use fast path for Xen timer delivery

Most of the time there's no need to kick the vCPU and deliver the timer
event through kvm_xen_inject_timer_irqs(). Use kvm_xen_set_evtchn_fast()
directly from the timer callback, and only fall back to the slow path if
delivering the timer would block, i.e. if kvm_xen_set_evtchn_fast()
returns -EWOULDBLOCK. If delivery fails for any other reason, do nothing
and just let it fail silently, as that is what the slow path would end up
doing anyways.

This gives a significant improvement in timer latency testing (using
nanosleep() for various periods and then measuring the actual time
elapsed).

However, there was a reason[1] the fast path was dropped when this support
was first added. The current code holds vcpu->mutex for all operations on
the kvm->arch.timer_expires field, and the fast path introduces a
potential race condition. Avoid that race by ensuring the hrtimer is
(temporarily) cancelled before making changes in kvm_xen_start_timer(),
and also when reading the values out for KVM_XEN_VCPU_ATTR_TYPE_TIMER.

[1] https://lore.kernel.org/kvm/846caa99-2e42-4443-1070-84e49d2f11d2@redhat.com

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/f21ee3bd852761e7808240d4ecaec3013c649dc7.camel@infradead.org
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86/xen: update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

The scaling information in subleaf 1 should match the values set by KVM in
the 'vcpu_info' sub-structure 'time_info' (a.k.a. pvclock_vcpu_time_info)
which is shared with the guest, but is not directly available to the VMM.
The offset values are not set since a TSC offset is already applied.
The TSC frequency should also be set in sub-leaf 2.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20230106103600.528-3-pdurrant@amazon.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86: Unify pr_fmt to use module name for all KVM modules

Define pr_fmt using KBUILD_MODNAME for all KVM x86 code so that printks
use consistent formatting across common x86, Intel, and AMD code. In
addition to providing consistent print formatting, using KBUILD_MODNAME,
e.g. kvm_amd and kvm_intel, allows referencing SVM and VMX (and SEV and
SGX and ...) as technologies without generating weird messages, and
without causing naming conflicts with other kernel code, e.g. "SEV: ",
"tdx: ", "sgx: " etc.. are all used by the kernel for non-KVM subsystems.

Opportunistically move away from printk() for prints that need to be
modified anyways, e.g. to drop a manual "kvm: " prefix.

Opportunistically convert a few SGX WARNs that are similarly modified to
WARN_ONCE; in the very unlikely event that the WARNs fire, odds are good
that they would fire repeatedly and spam the kernel log without providing
unique information in each print.

Note, defining pr_fmt yields undesirable results for code that uses KVM's
printk wrappers, e.g. vcpu_unimpl(). But, that's a pre-existing problem
as SVM/kvm_amd already defines a pr_fmt, and thankfully use of KVM's
wrappers is relatively limited in KVM x86 code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Message-Id: <20221130230934.1014142-35-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Avoid deadlock by adding kvm->arch.xen.xen_lock leaf node lock

In commit 14243b387137a ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN
and event channel delivery") the clever version of me left some helpful
notes for those who would come after him:

/*
* For the irqfd workqueue, using the main kvm->lock mutex is
* fine since this function is invoked from kvm_set_irq() with
* no other lock held, no srcu. In future if it will be called
* directly from a vCPU thread (e.g. on hypercall for an IPI)
* then it may need to switch to using a leaf-node mutex for
* serializing the shared_info mapping.
*/
mutex_lock(&kvm->lock);

In commit 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
the other version of me ran straight past that comment without reading it,
and introduced a potential deadlock by taking vcpu->mutex and kvm->lock
in the wrong order.

Solve this as originally suggested, by adding a leaf-node lock in the Xen
state rather than using kvm->lock for it.

Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20230111180651.14394-4-dwmw2@infradead.org>
[Rebase, add docs. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix potential deadlock in kvm_xen_update_runstate_guest()

The kvm_xen_update_runstate_guest() function can be called when the vCPU
is being scheduled out, from a preempt notifier. It *opportunistically*
updates the runstate area in the guest memory, if the gfn_to_pfn_cache
which caches the appropriate address is still valid.

If there is *contention* when it attempts to obtain gpc->lock, then
locking inside the priority inheritance checks may cause a deadlock.
Lockdep reports:

[13890.148997] Chain exists of:
&gpc->lock --> &p->pi_lock --> &rq->__lock

[13890.149002] Possible unsafe locking scenario:

[13890.149003] CPU0 CPU1
[13890.149004] ---- ----
[13890.149005] lock(&rq->__lock);
[13890.149007] lock(&p->pi_lock);
[13890.149009] lock(&rq->__lock);
[13890.149011] lock(&gpc->lock);
[13890.149013]
*** DEADLOCK ***

In the general case, if there's contention for a read lock on gpc->lock,
that's going to be because something else is either invalidating or
revalidating the cache. Either way, we've raced with seeing it in an
invalid state, in which case we would have aborted the opportunistic
update anyway.

So in the 'atomic' case when called from the preempt notifier, just
switch to using read_trylock() and avoid the PI handling altogether.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20230111180651.14394-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix lockdep warning on "recursive" gpc locking

In commit 5ec3289b31 ("KVM: x86/xen: Compatibility fixes for shared runstate
area") we declared it safe to obtain two gfn_to_pfn_cache locks at the same
time:
/*
* The guest's runstate_info is split across two pages and we
* need to hold and validate both GPCs simultaneously. We can
* declare a lock ordering GPC1 > GPC2 because nothing else
* takes them more than one at a time.
*/

However, we forgot to tell lockdep. Do so, by setting a subclass on the
first lock before taking the second.

Fixes: 5ec3289b31 ("KVM: x86/xen: Compatibility fixes for shared runstate area")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20230111180651.14394-1-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: fix deadlock for KVM_XEN_EVTCHN_RESET

While KVM_XEN_EVTCHN_RESET is usually called with no vCPUs running,
if that happened it could cause a deadlock. This is due to
kvm_xen_eventfd_reset() doing a synchronize_srcu() inside
a kvm->lock critical section.

To avoid this, first collect all the evtchnfd objects in an
array and free all of them once the kvm->lock critical section
is over and th SRCU grace period has expired.

Reported-by: Michal Luczaj <mhal@rbox.co>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add KVM_XEN_INVALID_GPA and KVM_XEN_INVALID_GFN to uapi

These are (uint64_t)-1 magic values are a userspace ABI, allowing the
shared info pages and other enlightenments to be disabled. This isn't
a Xen ABI because Xen doesn't let the guest turn these off except with
the full SHUTDOWN_soft_reset mechanism. Under KVM, the userspace VMM is
expected to handle soft reset, and tear down the kernel parts of the
enlightenments accordingly.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-5-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Simplify eventfd IOCTLs

Port number is validated in kvm_xen_setattr_evtchn().
Remove superfluous checks in kvm_xen_eventfd_assign() and
kvm_xen_eventfd_update().

Signed-off-by: Michal Luczaj <mhal@rbox.co>
Message-Id: <20221222203021.1944101-3-mhal@rbox.co>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-4-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix SRCU/RCU usage in readers of evtchn_ports

The evtchnfd structure itself must be protected by either kvm->lock or
SRCU. Use the former in kvm_xen_eventfd_update(), since the lock is
being taken anyway; kvm_xen_hcall_evtchn_send() instead is a reader and
does not need kvm->lock, and is called in SRCU critical section from the
kvm_x86_handle_exit function.

It is also important to use rcu_read_{lock,unlock}() in
kvm_xen_hcall_evtchn_send(), because idr_remove() will *not*
use synchronize_srcu() to wait for readers to complete.

Remove a superfluous if (kvm) check before calling synchronize_srcu()
in kvm_xen_eventfd_deassign() where kvm has been dereferenced already.

Co-developed-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-3-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use kvm_read_guest_virt() instead of open-coding it badly

In particular, we shouldn't assume that being contiguous in guest virtual
address space means being contiguous in guest *physical* address space.

In dropping the manual calls to kvm_mmu_gva_to_gpa_system(), also drop
the srcu_read_lock() that was around them. All call sites are reached
from kvm_xen_hypercall() which is called from the handle_exit function
with the read lock already held.

536395260 ("KVM: x86/xen: handle PV timers oneshot mode")
1a65105a5 ("KVM: x86/xen: handle PV spinlocks slowpath")

Fixes: 2fd6df2f2 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix memory leak in kvm_xen_write_hypercall_page()

Release page irrespectively of kvm_vcpu_write_guest() return value.

Suggested-by: Paul Durrant <paul@xen.org>
Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Message-Id: <20221220151454.712165-1-mhal@rbox.co>
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-1-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Keep the lock order consistent between SRCU and gpc spinlock

Acquire SRCU before taking the gpc spinlock in wait_pending_event() so as
to be consistent with all other functions that acquire both locks. It's
not illegal to acquire SRCU inside a spinlock, nor is there deadlock
potential, but in general it's preferable to order locks from least
restrictive to most restrictive, e.g. if wait_pending_event() needed to
sleep for whatever reason, it could do so while holding SRCU, but would
need to drop the spinlock.

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/CAPm50a++Cb=QfnjMZ2EnCj-Sb9Y4UM-=uOEtHAcjnNLCAAf-dQ@mail.gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: Drop @gpa from exported gfn=>pfn cache check() and refresh() helpers

Drop the @gpa param from the exported check()+refresh() helpers and limit
changing the cache's GPA to the activate path. All external users just
feed in gpc->gpa, i.e. this is a fancy nop.

Allowing users to change the GPA at check()+refresh() is dangerous as
those helpers explicitly allow concurrent calls, e.g. KVM could get into
a livelock scenario. It's also unclear as to what the expected behavior
should be if multiple tasks attempt to refresh with different GPAs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_refresh()

Make kvm_gpc_refresh() use kvm instance cached in gfn_to_pfn_cache.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
[sean: leave kvm_gpc_unmap() as-is]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_check()

Make kvm_gpc_check() use kvm instance cached in gfn_to_pfn_cache.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: Store immutable gfn_to_pfn_cache properties

Move the assignment of immutable properties @kvm, @vcpu, and @usage to
the initializer. Make _activate() and _deactivate() use stored values.

Note, @len is also effectively immutable for most cases, but not in the
case of the Xen runstate cache, which may be split across two pages and
the length of the first segment will depend on its address.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
[sean: handle @len in a separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>
[dwmw2: acknowledge that @len can actually change for some use cases]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: add support for 32-bit guests in SCHEDOP_poll

This patch introduces compat version of struct sched_poll for
SCHEDOP_poll sub-operation of sched_op hypercall, reads correct amount
of data (16 bytes in 32-bit case, 24 bytes otherwise) by using new
compat_sched_poll struct, copies it to sched_poll properly, and lets
rest of the code run as is.

Signed-off-by: Metin Kaya <metikaya@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

KVM: Shorten gfn_to_pfn_cache function names

Formalize "gpc" as the acronym and use it in function names.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add runstate tests for 32-bit mode and crossing page boundary

Torture test the cases where the runstate crosses a page boundary, and
and especially the case where it's configured in 32-bit mode and doesn't,
but then switching to 64-bit mode makes it go onto the second page.

To simplify this, make the KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST ioctl
also update the guest runstate area. It already did so if the actual
runstate changed, as a side-effect of kvm_xen_update_runstate(). So
doing it in the plain adjustment case is making it more consistent, as
well as giving us a nice way to trigger the update without actually
running the vCPU again and changing the values.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Allow XEN_RUNSTATE_UPDATE flag behaviour to be configured

Closer inspection of the Xen code shows that we aren't supposed to be
using the XEN_RUNSTATE_UPDATE flag unconditionally. It should be
explicitly enabled by guests through the HYPERVISOR_vm_assist hypercall.
If we randomly set the top bit of ->state_entry_time for a guest that
hasn't asked for it and doesn't expect it, that could make the runtimes
fail to add up and confuse the guest. Without the flag it's perfectly
safe for a vCPU to read its own vcpu_runstate_info; just not for one
vCPU to read *another's*.

I briefly pondered adding a word for the whole set of VMASST_TYPE_*
flags but the only one we care about for HVM guests is this, so it
seemed a bit pointless.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221127122210.248427-3-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Compatibility fixes for shared runstate area

The guest runstate area can be arbitrarily byte-aligned. In fact, even
when a sane 32-bit guest aligns the overall structure nicely, the 64-bit
fields in the structure end up being unaligned due to the fact that the
32-bit ABI only aligns them to 32 bits.

So setting the ->state_entry_time field to something|XEN_RUNSTATE_UPDATE
is buggy, because if it's unaligned then we can't update the whole field
atomically; the low bytes might be observable before the _UPDATE bit is.
Xen actually updates the *byte* containing that top bit, on its own. KVM
should do the same.

In addition, we cannot assume that the runstate area fits within a single
page. One option might be to make the gfn_to_pfn cache cope with regions
that cross a page — but getting a contiguous virtual kernel mapping of a
discontiguous set of IOMEM pages is a distinctly non-trivial exercise,
and it seems this is the *only* current use case for the GPC which would
benefit from it.

An earlier version of the runstate code did use a gfn_to_hva cache for
this purpose, but it still had the single-page restriction because it
used the uhva directly — because it needs to be able to do so atomically
when the vCPU is being scheduled out, so it used pagefault_disable()
around the accesses and didn't just use kvm_write_guest_cached() which
has a fallback path.

So... use a pair of GPCs for the first and potential second page covering
the runstate area. We can get away with locking both at once because
nothing else takes more than one GPC lock at a time so we can invent
a trivial ordering rule.

The common case where it's all in the same page is kept as a fast path,
but in both cases, the actual guest structure (compat or not) is built
up from the fields in @vx, following preset pointers to the state and
times fields. The only difference is whether those pointers point to
the kernel stack (in the split case) or to guest memory directly via
the GPC. The fast path is also fixed to use a byte access for the
XEN_RUNSTATE_UPDATE bit, then the only real difference is the dual
memcpy.

Finally, Xen also does write the runstate area immediately when it's
configured. Flip the kvm_xen_update_runstate() and …_guest() functions
and call the latter directly when the runstate area is set. This means
that other ioctls which modify the runstate also write it immediately
to the guest when they do so, which is also intended.

Update the xen_shinfo_test to exercise the pathological case where the
XEN_RUNSTATE_UPDATE flag in the top byte of the state_entry_time is
actually in a different page to the rest of the 64-bit word.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add CPL to Xen hypercall tracepoint

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Only do in-kernel acceleration of hypercalls for guest CPL0

There are almost no hypercalls which are valid from CPL > 0, and definitely
none which are handled by the kernel.

Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Reported-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Cc: stable@kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Validate port number in SCHEDOP_poll

We shouldn't allow guests to poll on arbitrary port numbers off the end
of the event channel table.

Fixes: 1a65105a5aba ("KVM: x86/xen: handle PV spinlocks slowpath")
[dwmw2: my bug though; the original version did check the validity as a
side-effect of an idr_find() which I ripped out in refactoring.]
Reported-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Cc: stable@kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix eventfd error handling in kvm_xen_eventfd_assign()

Should not call eventfd_ctx_put() in case of error.

Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Reported-by: syzbot+6f0c896c5a9449a10ded@syzkaller.appspotmail.com
Signed-off-by: Eiichi Tsukata <eiichi.tsukata@nutanix.com>
Message-Id: <20221028092631.117438-1-eiichi.tsukata@nutanix.com>
[Introduce new goto target instead. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: Initialize gfn_to_pfn_cache locks in dedicated helper

Move the gfn_to_pfn_cache lock initialization to another helper and
call the new helper during VM/vCPU creation. There are race
conditions possible due to kvm_gfn_to_pfn_cache_init()'s
ability to re-initialize the cache's locks.

For example: a race between ioctl(KVM_XEN_HVM_EVTCHN_SEND) and
kvm_gfn_to_pfn_cache_init() leads to a corrupted shinfo gpc lock.

(thread 1) | (thread 2)
|
kvm_xen_set_evtchn_fast |
read_lock_irqsave(&gpc->lock, ...) |
| kvm_gfn_to_pfn_cache_init
| rwlock_init(&gpc->lock)
read_unlock_irqrestore(&gpc->lock, ...) |

Rename "cache_init" and "cache_destroy" to activate+deactivate to
avoid implying that the cache really is destroyed/freed.

Note, there more races in the newly named kvm_gpc_activate() that will
be addressed separately.

Fixes: 982ed0de4753 ("KVM: Reinstate gfn_to_pfn_cache with invalidation support")
Cc: stable@vger.kernel.org
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
[sean: call out that this is a bug fix]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221013211234.1318131-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: remove KVM_REQ_UNHALT

KVM_REQ_UNHALT is now unnecessary because it is replaced by the return
value of kvm_vcpu_block/kvm_vcpu_halt. Remove it.

No functional change intended.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Message-Id: <20220921003201.1441511-13-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Stop Xen timer before changing IRQ

Stop Xen timer (if it's running) prior to changing the IRQ vector and
potentially (re)starting the timer. Changing the IRQ vector while the
timer is still running can result in KVM injecting a garbage event, e.g.
vm_xen_inject_timer_irqs() could see a non-zero xen.timer_pending from
a previous timer but inject the new xen.timer_virq.

Fixes: 536395260582 ("KVM: x86/xen: handle PV timers oneshot mode")
Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=8234a9dfd3aafbf092cc5a7cd9842e3ebc45fc42
Reported-by: syzbot+e54f930ed78eb0f85281@syzkaller.appspotmail.com
Signed-off-by: Coleman Dietsch <dietschc@csp.edu>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20220808190607.323899-3-dietschc@csp.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Initialize Xen timer only once

Add a check for existing xen timers before initializing a new one.

Currently kvm_xen_init_timer() is called on every
KVM_XEN_VCPU_ATTR_TYPE_TIMER, which is causing the following ODEBUG
crash when vcpu->arch.xen.timer is already set.

ODEBUG: init active (active state 0)
object type: hrtimer hint: xen_timer_callbac0
RIP: 0010:debug_print_object+0x16e/0x250 lib/debugobjects.c:502
Call Trace:
__debug_object_init
debug_hrtimer_init
debug_init
hrtimer_init
kvm_xen_init_timer
kvm_xen_vcpu_set_attr
kvm_arch_vcpu_ioctl
kvm_vcpu_ioctl
vfs_ioctl

Fixes: 536395260582 ("KVM: x86/xen: handle PV timers oneshot mode")
Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=8234a9dfd3aafbf092cc5a7cd9842e3ebc45fc42
Reported-by: syzbot+e54f930ed78eb0f85281@syzkaller.appspotmail.com
Signed-off-by: Coleman Dietsch <dietschc@csp.edu>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220808190607.323899-2-dietschc@csp.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Query vcpu->vcpu_idx directly and drop its accessor, again

Read vcpu->vcpu_idx directly instead of bouncing through the one-line
wrapper, kvm_vcpu_get_idx(), and drop the wrapper. The wrapper is a
remnant of the original implementation and serves no purpose; remove it
(again) before it gains more users.

kvm_vcpu_get_idx() was removed in the not-too-distant past by commit
4eeef2424153 ("KVM: x86: Query vcpu->vcpu_idx directly and drop its
accessor"), but was unintentionally re-introduced by commit a54d806688fe
("KVM: Keep memslots in tree-based structures instead of array-based ones"),
likely due to a rebase goof. The wrapper then managed to gain users in
KVM's Xen code.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20220614225615.3843835-1-seanjc@google.com

KVM: x86/xen: Remove the redundantly included header file lapic.h

The header lapic.h is included more than once, remove one of them.

Signed-off-by: Like Xu <likexu@tencent.com>
Message-Id: <20220406063715.55625-2-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: handle PV spinlocks slowpath

Add support for SCHEDOP_poll hypercall.

This implementation is optimized for polling for a single channel, which
is what Linux does. Polling for multiple channels is not especially
efficient (and has not been tested).

PV spinlocks slow path uses this hypercall, and explicitly crash if it's
not supported.

[ dwmw2: Rework to use kvm_vcpu_halt(), not supported for 32-bit guests ]

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-17-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Advertise and document KVM_XEN_HVM_CONFIG_EVTCHN_SEND

At the end of the patch series adding this batch of event channel
acceleration features, finally add the feature bit which advertises
them and document it all.

For SCHEDOP_poll we need to wake a polling vCPU when a given port
is triggered, even when it's masked — and we want to implement that
in the kernel, for efficiency. So we want the kernel to know that it
has sole ownership of event channel delivery. Thus, we allow
userspace to make the 'promise' by setting the corresponding feature
bit in its KVM_XEN_HVM_CONFIG call. As we implement SCHEDOP_poll
bypass later, we will do so only if that promise has been made by
userspace.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-16-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Support per-vCPU event channel upcall via local APIC

Windows uses a per-vCPU vector, and it's delivered via the local APIC
basically like an MSI (with associated EOI) unlike the traditional
guest-wide vector which is just magically asserted by Xen (and in the
KVM case by kvm_xen_has_interrupt() / kvm_cpu_get_extint()).

Now that the kernel is able to raise event channel events for itself,
being able to do so for Windows guests is also going to be useful.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-15-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Kernel acceleration for XENVER_version

Turns out this is a fast path for PV guests because they use it to
trigger the event channel upcall. So letting it bounce all the way up
to userspace is not great.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-14-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: handle PV timers oneshot mode

If the guest has offloaded the timer virq, handle the following
hypercalls for programming the timer:

VCPUOP_set_singleshot_timer
VCPUOP_stop_singleshot_timer
set_timer_op(timestamp_ns)

The event channel corresponding to the timer virq is then used to inject
events once timer deadlines are met. For now we back the PV timer with
hrtimer.

[ dwmw2: Add save/restore, 32-bit compat mode, immediate delivery,
don't check timer in kvm_vcpu_has_event() ]

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-13-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID

In order to intercept hypercalls such as VCPUOP_set_singleshot_timer, we
need to be aware of the Xen CPU numbering.

This looks a lot like the Hyper-V handling of vpidx, for obvious reasons.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-12-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: handle PV IPI vcpu yield

Cooperative Linux guests after an IPI-many may yield vcpu if
any of the IPI'd vcpus were preempted (i.e. runstate is 'runnable'.)
Support SCHEDOP_yield for handling yield.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-11-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: intercept EVTCHNOP_send from guests

Userspace registers a sending @port to either deliver to an @eventfd
or directly back to a local event channel port.

After binding events the guest or host may wish to bind those
events to a particular vcpu. This is usually done for unbound
and and interdomain events. Update requests are handled via the
KVM_XEN_EVTCHN_UPDATE flag.

Unregistered ports are handled by the emulator.

Co-developed-by: Ankur Arora <ankur.a.arora@oracle.com>
Co-developed-By: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-10-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Support direct injection of event channel events

This adds a KVM_XEN_HVM_EVTCHN_SEND ioctl which allows direct injection
of events given an explicit { vcpu, port, priority } in precisely the
same form that those fields are given in the IRQ routing table.

Userspace is currently able to inject 2-level events purely by setting
the bits in the shared_info and vcpu_info, but FIFO event channels are
harder to deal with; we will need the kernel to take sole ownership of
delivery when we support those.

A patch advertising this feature with a new bit in the KVM_CAP_XEN_HVM
ioctl will be added in a subsequent patch.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-9-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Make kvm_xen_set_evtchn() reusable from other places

Clean it up to return -errno on error consistently, while still being
compatible with the return conventions for kvm_arch_set_irq_inatomic()
and the kvm_set_irq() callback.

We use -ENOTCONN to indicate when the port is masked. No existing users
care, except that it's negative.

Also allow it to optimise the vCPU lookup. Unless we abuse the lapic
map, there is no quick lookup from APIC ID to a vCPU; the logic in
kvm_get_vcpu_by_id() will just iterate over all vCPUs till it finds
the one it wants. So do that just once and stash the result in the
struct kvm_xen_evtchn for next time.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-8-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use gfn_to_pfn_cache for vcpu_time_info

This switches the final pvclock to kvm_setup_pvclock_pfncache() and now
the old kvm_setup_pvclock_page() can be removed.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-7-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use gfn_to_pfn_cache for vcpu_info

Currently, the fast path of kvm_xen_set_evtchn_fast() doesn't set the
index bits in the target vCPU's evtchn_pending_sel, because it only has
a userspace virtual address with which to do so. It just sets them in
the kernel, and kvm_xen_has_interrupt() then completes the delivery to
the actual vcpu_info structure when the vCPU runs.

Using a gfn_to_pfn_cache allows kvm_xen_set_evtchn_fast() to do the full
delivery in the common case.

Clean up the fallback case too, by moving the deferred delivery out into
a separate kvm_xen_inject_pending_events() function which isn't ever
called in atomic contexts as __kvm_xen_has_interrupt() is.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-6-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use gfn_to_pfn_cache for runstate area

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-4-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: Remove dirty handling from gfn_to_pfn_cache completely

It isn't OK to cache the dirty status of a page in internal structures
for an indefinite period of time.

Any time a vCPU exits the run loop to userspace might be its last; the
VMM might do its final check of the dirty log, flush the last remaining
dirty pages to the destination and complete a live migration. If we
have internal 'dirty' state which doesn't get flushed until the vCPU
is finally destroyed on the source after migration is complete, then
we have lost data because that will escape the final copy.

This problem already exists with the use of kvm_vcpu_unmap() to mark
pages dirty in e.g. VMX nesting.

Note that the actual Linux MM already considers the page to be dirty
since we have a writeable mapping of it. This is just about the KVM
dirty logging.

For the nesting-style use cases (KVM_GUEST_USES_PFN) we will need to
track which gfn_to_pfn_caches have been used and explicitly mark the
corresponding pages dirty before returning to userspace. But we would
have needed external tracking of that anyway, rather than walking the
full list of GPCs to find those belonging to this vCPU which are dirty.

So let's rely *solely* on that external tracking, and keep it simple
rather than laying a tempting trap for callers to fall into.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-3-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: Use enum to track if cached PFN will be used in guest and/or host

Replace the guest_uses_pa and kernel_map booleans in the PFN cache code
with a unified enum/bitmask. Using explicit names makes it easier to
review and audit call sites.

Opportunistically add a WARN to prevent passing garbage; instantating a
cache without declaring its usage is either buggy or pointless.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: xen: Use static_call() for invoking kvm_x86_ops hooks

Use static_call() for invoking kvm_x86_ops function that already have a
defined static call, mostly as a step toward having _all_ calls to
kvm_x86_ops route through a static_call() in order to simplify auditing,
e.g. via grep, that all functions have an entry in kvm-x86-ops.h, but
also because there's no reason not to use a static_call().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220128005208.4008533-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix runstate updates to be atomic when preempting vCPU

There are circumstances whem kvm_xen_update_runstate_guest() should not
sleep because it ends up being called from __schedule() when the vCPU
is preempted:

[ 222.830825] kvm_xen_update_runstate_guest+0x24/0x100
[ 222.830878] kvm_arch_vcpu_put+0x14c/0x200
[ 222.830920] kvm_sched_out+0x30/0x40
[ 222.830960] __schedule+0x55c/0x9f0

To handle this, make it use the same trick as __kvm_xen_has_interrupt(),
of using the hva from the gfn_to_hva_cache directly. Then it can use
pagefault_disable() around the accesses and just bail out if the page
is absent (which is unlikely).

I almost switched to using a gfn_to_pfn_cache here and bailing out if
kvm_map_gfn() fails, like kvm_steal_time_set_preempted() does — but on
closer inspection it looks like kvm_map_gfn() will *always* fail in
atomic context for a page in IOMEM, which means it will silently fail
to make the update every single time for such guests, AFAICT. So I
didn't do it that way after all. And will probably fix that one too.

Cc: stable@vger.kernel.org
Fixes: 30b5c851af79 ("KVM: x86/xen: Add support for vCPU runstate information")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <b17a93e5ff4561e57b1238e3e7ccd0b613eb827e.camel@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

x86,kvm/xen: Remove superfluous .fixup usage

Commit 14243b387137 ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and
event channel delivery") adds superfluous .fixup usage after the whole
.fixup section was removed in commit e5eefda5aa51 ("x86: Remove .fixup
section").

Fixes: 14243b387137 ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and event channel delivery")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Message-Id: <20220123124219.GH20638@worktop.programming.kicks-ass.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Fix wall clock writes in Xen shared_info not to mark page dirty

When dirty ring logging is enabled, any dirty logging without an active
vCPU context will cause a kernel oops. But we've already declared that
the shared_info page doesn't get dirty tracking anyway, since it would
be kind of insane to mark it dirty every time we deliver an event channel
interrupt. Userspace is supposed to just assume it's always dirty any
time a vCPU can run or event channels are routed.

So stop using the generic kvm_write_wall_clock() and just write directly
through the gfn_to_pfn_cache that we already have set up.

We can make kvm_write_wall_clock() static in x86.c again now, but let's
not remove the 'sec_hi_ofs' argument even though it's not used yet. At
some point we *will* want to use that for KVM guests too.

Fixes: 629b5348841a ("KVM: x86/xen: update wallclock region")
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211210163625.2886-6-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and event channel delivery

This adds basic support for delivering 2 level event channels to a guest.

Initially, it only supports delivery via the IRQ routing table, triggered
by an eventfd. In order to do so, it has a kvm_xen_set_evtchn_fast()
function which will use the pre-mapped shared_info page if it already
exists and is still valid, while the slow path through the irqfd_inject
workqueue will remap the shared_info page if necessary.

It sets the bits in the shared_info page but not the vcpu_info; that is
deferred to __kvm_xen_has_interrupt() which raises the vector to the
appropriate vCPU.

Add a 'verbose' mode to xen_shinfo_test while adding test cases for this.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211210163625.2886-5-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Maintain valid mapping of Xen shared_info page

Use the newly reinstated gfn_to_pfn_cache to maintain a kernel mapping
of the Xen shared_info page so that it can be accessed in atomic context.

Note that we do not participate in dirty tracking for the shared info
page and we do not explicitly mark it dirty every single tim we deliver
an event channel interrupts. We wouldn't want to do that even if we *did*
have a valid vCPU context with which to do so.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211210163625.2886-4-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Assume a 64-bit hypercall for guests with protected state

When processing a hypercall for a guest with protected state, currently
SEV-ES guests, the guest CS segment register can't be checked to
determine if the guest is in 64-bit mode. For an SEV-ES guest, it is
expected that communication between the guest and the hypervisor is
performed to shared memory using the GHCB. In order to use the GHCB, the
guest must have been in long mode, otherwise writes by the guest to the
GHCB would be encrypted and not be able to be comprehended by the
hypervisor.

Create a new helper function, is_64_bit_hypercall(), that assumes the
guest is in 64-bit mode when the guest has protected state, and returns
true, otherwise invoking is_64_bit_mode() to determine the mode. Update
the hypercall related routines to use is_64_bit_hypercall() instead of
is_64_bit_mode().

Add a WARN_ON_ONCE() to is_64_bit_mode() to catch occurences of calls to
this helper function for a guest running with protected state.

Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
Reported-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <e0b20c770c9d0d1403f23d83e785385104211f74.1621878537.git.thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use sizeof_field() instead of open-coding it

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211115165030.7422-4-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix get_attr of KVM_XEN_ATTR_TYPE_SHARED_INFO

In commit 319afe68567b ("KVM: xen: do not use struct gfn_to_hva_cache") we
stopped storing this in-kernel as a GPA, and started storing it as a GFN.
Which means we probably should have stopped calling gpa_to_gfn() on it
when userspace asks for it back.

Cc: stable@vger.kernel.org
Fixes: 319afe68567b ("KVM: xen: do not use struct gfn_to_hva_cache")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211115165030.7422-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix kvm_xen_has_interrupt() sleeping in kvm_vcpu_block()

In kvm_vcpu_block, the current task is set to TASK_INTERRUPTIBLE before
making a final check whether the vCPU should be woken from HLT by any
incoming interrupt.

This is a problem for the get_user() in __kvm_xen_has_interrupt(), which
really shouldn't be sleeping when the task state has already been set.
I think it's actually harmless as it would just manifest itself as a
spurious wakeup, but it's causing a debug warning:

[ 230.963649] do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000b6bcdbc9>] prepare_to_swait_exclusive+0x30/0x80

Fix the warning by turning it into an *explicit* spurious wakeup. When
invoked with !task_is_running(current) (and we might as well add
in_atomic() there while we're at it), just return 1 to indicate that
an IRQ is pending, which will cause a wakeup and then something will
call it again in a context that *can* sleep so it can fault the page
back in.

Cc: stable@vger.kernel.org
Fixes: 40da8ccd724f ("KVM: x86/xen: Add event channel interrupt vector upcall")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Message-Id: <168bf8c689561da904e48e2ff5ae4713eaef9e2d.camel@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: xen: do not use struct gfn_to_hva_cache

gfn_to_hva_cache is not thread-safe, so it is usually used only within
a vCPU (whose code is protected by vcpu->mutex). The Xen interface
implementation has such a cache in kvm->arch, but it is not really
used except to store the location of the shared info page. Replace
shinfo_set and shinfo_cache with just the value that is passed via
KVM_XEN_ATTR_TYPE_SHARED_INFO; the only complication is that the
initialization value is not zero anymore and therefore kvm_xen_init_vm
needs to be introduced.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Rename GPR accessors to make mode-aware variants the defaults

Append raw to the direct variants of kvm_register_read/write(), and
drop the "l" from the mode-aware variants. I.e. make the mode-aware
variants the default, and make the direct variants scary sounding so as
to discourage use. Accessing the full 64-bit values irrespective of
mode is rarely the desired behavior.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210422022128.3464144-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Drop RAX[63:32] when processing hypercall

Truncate RAX to 32 bits, i.e. consume EAX, when retrieving the hypecall
index for a Xen hypercall. Per Xen documentation[*], the index is EAX
when the vCPU is not in 64-bit mode.

[*] http://xenbits.xenproject.org/docs/sphinx-unstable/guest-guide/x86/hypercall-abi.html

Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210422022128.3464144-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add support for vCPU runstate information

This is how Xen guests do steal time accounting. The hypervisor records
the amount of time spent in each of running/runnable/blocked/offline
states.

In the Xen accounting, a vCPU is still in state RUNSTATE_running while
in Xen for a hypercall or I/O trap, etc. Only if Xen explicitly schedules
does the state become RUNSTATE_blocked. In KVM this means that even when
the vCPU exits the kvm_run loop, the state remains RUNSTATE_running.

The VMM can explicitly set the vCPU to RUNSTATE_blocked by using the
KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_CURRENT attribute, and can also use
KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST to retrospectively add a given
amount of time to the blocked state and subtract it from the running
state.

The state_entry_time corresponds to get_kvmclock_ns() at the time the
vCPU entered the current state, and the total times of all four states
should always add up to state_entry_time.

Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20210301125309.874953-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Fix return code when clearing vcpu_info and vcpu_time_info

When clearing the per-vCPU shared regions, set the return value to zero
to indicate success. This was causing spurious errors to be returned to
userspace on soft reset.

Also add a paranoid BUILD_BUG_ON() for compat structure compatibility.

Fixes: 0c165b3c01fe ("KVM: x86/xen: Allow reset of Xen attributes")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20210301125309.874953-1-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Allow reset of Xen attributes

In order to support Xen SHUTDOWN_soft_reset (for guest kexec, etc.) the
VMM needs to be able to tear everything down and return the Xen features
to a clean slate.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20210208232326.1830370-1-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: hyper-v: Make Hyper-V emulation enablement conditional

Hyper-V emulation is enabled in KVM unconditionally. This is bad at least
from security standpoint as it is an extra attack surface. Ideally, there
should be a per-VM capability explicitly enabled by VMM but currently it
is not the case and we can't mandate one without breaking backwards
compatibility. We can, however, check guest visible CPUIDs and only enable
Hyper-V emulation when "Hv#1" interface was exposed in
HYPERV_CPUID_INTERFACE.

Note, VMMs are free to act in any sequence they like, e.g. they can try
to set MSRs first and CPUIDs later so we still need to allow the host
to read/write Hyper-V specific MSRs unconditionally.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210126134816.1880136-14-vkuznets@redhat.com>
[Add selftest vcpu_set_hv_cpuid API to avoid breaking xen_vmcall_test. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Use hva_t for holding hypercall page address

Use hva_t, a.k.a. unsigned long, for the local variable that holds the
hypercall page address. On 32-bit KVM, gcc complains about using a u64
due to the implicit cast from a 64-bit value to a 32-bit pointer.

arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
different size [-Werror=int-to-pointer-cast]
300 | page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210208201502.1239867-1-seanjc@google.com>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Remove extra unlock in kvm_xen_hvm_set_attr()

This accidentally ended up locking and then immediately unlocking kvm->lock
at the beginning of the function. Fix it.

Fixes: a76b9641ad1c ("KVM: x86/xen: add KVM_XEN_HVM_SET_ATTR/KVM_XEN_HVM_GET_ATTR")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20210208232326.1830370-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86/xen: Add event channel interrupt vector upcall

It turns out that we can't handle event channels *entirely* in userspace
by delivering them as ExtINT, because KVM is a bit picky about when it
accepts ExtINT interrupts from a legacy PIC. The in-kernel local APIC
has to have LVT0 configured in APIC_MODE_EXTINT and unmasked, which
isn't necessarily the case for Xen guests especially on secondary CPUs.

To cope with this, add kvm_xen_get_interrupt() which checks the
evtchn_pending_upcall field in the Xen vcpu_info, and delivers the Xen
upcall vector (configured by KVM_XEN_ATTR_TYPE_UPCALL_VECTOR) if it's
set regardless of LAPIC LVT0 configuration. This gives us the minimum
support we need for completely userspace-based implementation of event
channels.

This does mean that vcpu_enter_guest() needs to check for the
evtchn_pending_upcall flag being set, because it can't rely on someone
having set KVM_REQ_EVENT unless we were to add some way for userspace to
do so manually.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: register vcpu time info region

Allow the Xen emulated guest the ability to register secondary
vcpu time information. On Xen guests this is used in order to be
mapped to userspace and hence allow vdso gettimeofday to work.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: setup pvclock updates

Parameterise kvm_setup_pvclock_page() a little bit so that it can be
invoked for different gfn_to_hva_cache structures, and with different
offsets. Then we can invoke it for the normal KVM pvclock and also for
the Xen one in the vcpu_info.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: register vcpu info

The vcpu info supersedes the per vcpu area of the shared info page and
the guest vcpus will use this instead.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: Add KVM_XEN_VCPU_SET_ATTR/KVM_XEN_VCPU_GET_ATTR

This will be used for per-vCPU setup such as runstate and vcpu_info.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: update wallclock region

Wallclock on Xen is written in the shared_info page.

To that purpose, export kvm_write_wall_clock() and pass on the GPA of
its location to populate the shared_info wall clock data.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: register shared_info page

Add KVM_XEN_ATTR_TYPE_SHARED_INFO to allow hypervisor to know where the
guest's shared info page is.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: latch long_mode when hypercall page is set up

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: add KVM_XEN_HVM_SET_ATTR/KVM_XEN_HVM_GET_ATTR

This will be used to set up shared info pages etc.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: Add kvm_xen_enabled static key

The code paths for Xen support are all fairly lightweight but if we hide
them behind this, they're even *more* lightweight for any system which
isn't actually hosting Xen guests.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: Move KVM_XEN_HVM_CONFIG handling to xen.c

This is already more complex than the simple memcpy it originally had.
Move it to xen.c with the rest of the Xen support.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: Fix coexistence of Xen and Hyper-V hypercalls

Disambiguate Xen vs. Hyper-V calls by adding 'orl $0x80000000, %eax'
at the start of the Hyper-V hypercall page when Xen hypercalls are
also enabled.

That bit is reserved in the Hyper-V ABI, and those hypercall numbers
will never be used by Xen (because it does precisely the same trick).

Switch to using kvm_vcpu_write_guest() while we're at it, instead of
open-coding it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

KVM: x86/xen: intercept xen hypercalls if enabled

Add a new exit reason for emulator to handle Xen hypercalls.

Since this means KVM owns the ABI, dispense with the facility for the
VMM to provide its own copy of the hypercall pages; just fill them in
directly using VMCALL/VMMCALL as we do for the Hyper-V hypercall page.

This behaviour is enabled by a new INTERCEPT_HCALL flag in the
KVM_XEN_HVM_CONFIG ioctl structure, and advertised by the same flag
being returned from the KVM_CAP_XEN_HVM check.

Rename xen_hvm_config() to kvm_xen_write_hypercall_page() and move it
to the nascent xen.c while we're at it, and add a test case.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>